1. Field of the Invention
The present invention relates to a bar code label in which information on each of various goods, outdoor installations, individuals or the like is recorded as engraving in the form of characters and bar codes. The invention also relates to readers for the bar code labels.
2. Description of the Prior Art
Bar code labels are well known and widely used attached on the surface of a box or package in which goods or a delivery is packed. The bar code label carries a variety of information coded in the form of bars different in width from one another. The information is used for a higher efficiency and less labor in sales calculation, inventory control or sorting.
Generally, such bar code is black bars printed on the white surface of a bar code label. If the label surface is stained with an oil or dirt or if the blackness of the coded bars fades. The information recorded in the bar code label cannot possibly be read positively and accurately. Particularly, there is a problem in reading the bar code label outdoors.
Recently, a magnetic bar code reading system has been proposed which can be used in any environment. In this system, engraved recesses (characters and bar codes) 202, 202', 203, . . . are made, as shown in FIG. 1, on a bar code label 201 made of a metal such as iron and the recesses are magnetically detected by means of a ferromagnetic magnetic resistance device referred to as "MR device" hereinafter) and a permanent magnet. More particularly, the head at the bottom of a main body 204 in which the MR device and permanent magnet are integrally incorporated is swept across the engraved bar code label 201 to read the recess pattern consisting of the recesses 202, 202', 203 , . . . The principle of this bar code reading will be discussed below.
When the head is placed on the engraved bar code label 201, the engraved recesses 202, 202', 203, . . . are magnetized by the DC magnetic field formed by the permanent magnet. The magnetic field formed by these magnetized recesses causes the magnetic flux distribution over the recesses to change and these changes of the magnetic flux distribution result in resistance changes of the MR device. The resistance changes are passed to the signal processing circuit provided in the head of the main body 204 in which they are converted into binary-coded (0 or 1) signal corresponding to the code represented by the recess pattern. This binary-coded signal is supplied to the decoder for recognition of the bar code pattern.
The conventional head of the magnetic bar code reader operating on the above-mentioned principle has a tip of which the structure will be discussed below with reference to FIG. 2. Namely, for an electrical connection between an input wire of an MR device 206 made on a printed circuit board 205 through a well-known IC manufacturing process and an external lead wire 207 through which a current is supplied to detect a magnetic field change as a voltage, the circuit board 205 is connected to an electrode 209 by means of a bonding wire 208 and the external lead wire 207 is spot-joined to the electrode 209 by means of a solder joint 210. The electrode 209 and circuit board 205 are attached to an internal substrate 211. Further, the internal substrate 211 and electrode 209 are attached to a head frame 212 and sealed from below with a coating film 213. A permanent magnet 214 provided for exciting is attached to the internal substrate 211 and sealed with a coating film 215.
As the conventional sensor of the magnetic bar code reader operating on the above-mentioned principle, a generally square MR device is used as shown in FIG. 3. As seen, a magnetic resistance film 217 formed on a circuit board 216 made of, for example, a glass is provided in such a structure that it is folded back in parallel to the lateral side of the circuit board 216. For a high magnetic sensitivity, a plurality of such magnetic resistance films cascade-connected is provided. Usually, the number of the magnetic resistance films thus provided is such that the whole resistance will be on the order several kiloohms. Furthermore, a current-supplying electrode 218 is provided on either end of the magnetic resistance film 217 in such a manner that an ohmic contact can be assured. For a higher yield of manufacture with a reduced IC area, these patterns are so set as to form together a generally square shape in many cases.
In a magnetic bar code reader, the above-mentioned MR device is inclined more than 30 deg. with respect to bar code recesses 219 and a permanent magnet 220 which applies a biasing magnetic field is provided on the MR device to make a head 221 which will be swept across recesses 223, engraved in the form of bar code in an iron sheet 222, in a direction perpendicular to the length of the engraved recesses 223, thereby reading the bar code.
A bar code label made of any other metal sheet than the iron sheet is so resistant against contamination or staining that even when the label surface is stained with dirt or the like, it can be washed with water to remove such dirt. However, in case the label is made of an iron sheet, it will be rusty and thus corroded. Particularly, any iron-sheet bar code label is not suitably usable in a place where the atmosphere is very salty.
In the head having the structure shown in FIG. 2, since the bonding wire 208 is bonded to the electrode 205 on the substrate (semiconductor substrate) of the MR device 206 by using an ultrasonic bonder or the like, an air gap d (about 0.3 mm) must be provided under these elements. This air gap causes the strength of the magnetic lines of force produced by the engraved recesses, that is to be detected by the MR device, to be extremely small. In other words, the MR device has only a low sensitivity to the magnetic lines of force formed by the bar code recesses. When the head is off the bar code label, the sensitivity of the MR device is found to very low. For example, when the head is about 0.1 mm off the label surface in relation to a pattern of recesses of a minimum of 0.5 mm, the head can hardly read the code represented by the recess pattern.
In the bar code reader having a magnetic sensor of a structure shown in FIG. 3, since the magnetic resistance film 27 inside the reader is so large as to extend fully across one engraved recess, so the changes of magnetic field in opposite directions at the right and left recess edges cancels the magnetic resistance change of the MR device. Thus, this reader cannot read any high resolution engraved bar code composed of narrow recesses. For example, a common MR device of 0.5 to 0.6 mm in length and width should preferably be inclined 45 deg. with respect to the length of the recesses to apply a biasing magnetic field longitudinally of the recesses in order to read the bar code with a high sensitivity. In this case, however, the width of the MR device will be about 0.7 mm to 0.85 mm and thus it is apparent that the MR device cannot read any engraved recess of 0.5 mm in minimum width. Also even if a bar code reading head is constructed with the MR device not inclined 45 deg. (the biasing magnetic field may be applied from a direction inclined 45 deg.) but directed longitudinally of the engraved recesses at the sacrifice of the sensitivity to some extent, any common magnetic sensor element having a large width fitted in the head cannot read a high resolution (namely, narrow) bar code recess pattern.